The invention is based on an adjustable hydrostatic pump.
German Utility Model DE-GM Yt 04 126 discloses such a pump, in an embodiment as a radial piston pump, in which as the adjusting device, a cam ring is provided, whose eccentricity is considered the definitive variable for the pump adjustment or pump swiveling. The cam ring is retained in position by two different-sized hydraulic adjusting pistons, of which the larger adjusting piston is part of a hydromechanical adjusting assembly. The noise produced by such a piston pump is. very greatly dependent on the rigidity of the hydraulic fastening of the adjusting device, that is, the cam ring. The noise produced increases as the rigidity of the hydraulic fastening of the cam ring lessens and is caused by the components of the power-train forces acting in the direction of the adjustment. Depending on the rigidity of the fastening, this leads to a more or less pronounced deflection of the entire power train at the pace of the piston as it moves in and out of the pump pressure chamber. The noises that occur then may be annoying in some applications, where especially quiet operation is desired. Comparable conditions to the radial piston pump pertain to the axial piston pump as well, in which the adjusting device is embodied as a swash plate, and to a vane cell pump, which likewise has a cam ring as its adjusting device.
In a prior German patent application P 44 10 719.6, it has also already been proposed, in an adjustable radial piston pump, to provide active noise abatement, but here the adjustment of the cam ring is done via an electrohydraulic closed-loop control device. The intervention for noise abatement is done here via an electrohydraulic control valve, but many adjustable hydrostatic pumps lack such a valve.
From German patent disclosure OF 37 CO 573 A1, a radial piston engine is also known, in which an additional combustion chamber in the control journal can be charged from the high-pressure side via a throttled connection. As a function of the rotary position, the piston bore in the rotor is made to communicate briefly with this combustion chamber, and a rise in pressure is effected before this piston bore comes to communicate with the actual high-pressure control slit. In various cases, the noise reduction attendant on the lessening of the feed flow pulsation is insufficient, especially since the abrupt changes in force that occur as the piston emerges from the high-pressure side cannot be taken into account. No further description of the nature of the adjusting assembly is provided.